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                     Mission to Asteroid, Mars, and Comet Delayed
                               April 20, 1998

                    Software Troubles and Late Electronics System
                      Force NASA To Postpone Deep Space 1

                  The planned July 1998 launch of NASA's Deep Space
                  1 technology validation mission from Cape
                  Canaveral, Florida, has been rescheduled for
                  October.

                  The delay is due to a combination of late delivery
                  of the spacecraft's power electronics system and
                  an ambitious flight software development schedule,
                  which together leave insufficient time to test the
                  spacecraft thoroughly for a July launch.

                  The power electronics system regulates and
                  distributes power produced by not only the solar
                  concentrator array, a pair of experimental solar
                  panels composed of 720 cylindrical Fresnel lenses,
                  but also by an on-board battery. Among many other
                  functions, it helps the solar array to operate at
                  peak efficiency, and ensures that the battery is
                  able to cover temporary surges in power needed so
                  that the ion propulsion system (which needs
                  electricity for its basic operations) receives a
                  steady power supply.

                  "With a new launch date for this bold mission, we
                  can be more confident that we will be ready to
                  fully exercise our payload of important
                  technologies," explained Chief Mission Engineer
                  Marc Rayman of NASA's Jet Propulsion Laboratory in
                  Pasadena, California. "The entire DS1 team looks
                  forward to this opportunity to make a significant
                  contribution to science missions of the future
                  through the capabilities we are testing on DS1."

                  Deep Space 1 is the first launch in NASA's New
                  Millennium program, a series of missions designed
                  to test new technologies so that they can be
                  confidently used on science missions of the 21st
                  century. Among the 12 technologies the mission is
                  designed to validate are ion propulsion,
                  autonomous optical navigation, a solar power
                  concentrator array and an integrated camera and
                  imaging spectrometer.

                  The earlier July launch period for DS1 allowed it
                  to fly a trajectory encompassing flybys of an
                  asteroid, Mars, and a comet. By the end of May,
                  the mission design team is scheduled to finalize
                  new target bodies in the solar system for DS1 to
                  encounter based on an October launch date.


                  Editor's note: Deep Space 1 will no longer visit
                  asteroid 3352 McAuliffe, Mars, and comet
                  West-Kohoutek-lkemura. The launch delay was
                  announced after this article went to press.
                  Mission planners will announce the new targets for
                  this mission by the end of May. The full text and
                  graphics for this article will appear in the
                  May/June 1998 issue of The Planetary Report. This
                  publication goes out to all members of the
                  Planetary Society. If you're not already a member,
                  we encourage you to join.

                   Deep Space 1: Exploration Technology for the 21st
                                        Century

                                  by Robert M. Nelson
                                          and
                                    Marc D. Rayman

                       This summer NASA takes a revolutionary
                       step when it launches Deep Space 1
                       (DS1). During its flight, the spacecraft
                       will visit asteroid 3352 McAuliffe, the
                       planet Mars, and comet
                       West-Kohoutek-lkemura. But its primary
                       goal is not to study these fascinating
                       bodies; rather, as a member of the New
                       Millennium program, its job is to pave
                       the way for future, even more exciting,
                       space science missions.

                       NASA has already flown missions to
                       asteroids, comets, and Mars, so what
                       makes DS1 unusual? It will demonstrate a
                       dozen technical innovations that will
                       serve as foundation technologies for the
                       next generation of deep-space missions.
                       Foremost among these new technologies
                       will be solar electric propulsion (SEP),
                       which will enable a whole class of
                       ambitious missions that are simply
                       impractical or unaffordable, with the
                       standard chemical propulsion available
                       today.

                       A Test Drive

                       DS1 will be launched from Cape Canaveral
                       on the first Delta 7326 rocket, a
                       low-cost member of the Delta 11 family.
                       DS1 is so small that even this
                       economy-class launch vehicle will be
                       able to carry a second spacecraft --
                       SEDSAT-1, an Earth orbiter built at the
                       same time by students at the University
                       of Alabama in Huntsville.

                       Once in space, DS1 will be checked out
                       and certified by the mission operations
                       team, and then the SEP system will begin
                       thrusting. Instead of burning a strong,
                       short pulse of chemical propellant,
                       followed by a long interplanetary
                       cruise, the SEP system will sustain a
                       tenuous but very high-velocity stream of
                       ionized xenon. This stream will create a
                       gentle, steady thrust that will propel
                       the spacecraft almost continuously
                       during interplanetary cruise.

                       Although the thrust of SEP is small, its
                       advantage accrues because the exhaust
                       velocity of the ion rocket is many times
                       greater than the exhaust velocity of a
                       conventional chemical system. The bottom
                       line is that SEP requires far less
                       propellant than a chemical rocket to
                       deliver the same payload mass to a
                       target, It takes time for the gentle
                       thrust to build up high spacecraft
                       velocity, so SEP is appropriate only for
                       missions requiring high energy or long
                       trips.

                       Within a month of launch, DS1 will have
                       accomplished most of its major
                       objectives, and we will have assessed
                       its payload of advanced technologies. If
                       a technology fails during the flight,
                       even if it causes the loss of the
                       spacecraft, we may still regard the
                       mission as a success if it achieves the
                       program goal of reducing the risk for
                       future science missions. It is in these
                       future missions that the real science
                       return of DS1 will be found. But this
                       high-risk project will attempt to return
                       science during its test flight....

                       The flight of DS1 will test new autonomy
                       technologies, solar concentrator arrays,
                       and a variety of telecommunications and
                       microelectronics devices. Autonomy,
                       which in this case means the ability of
                       the spacecraft to make its own
                       decisions, can help reduce the heavy
                       burden on NASA's Deep Space Network
                       (DSN). As more and more probes are sent
                       into space in the coming years, it will
                       be harder for the DSN to communicate
                       with all of them as frequently as it has
                       done in the past. With autonomy
                       technologies allowing spacecraft to
                       operate for longer times without
                       detailed instructions from Earth, the
                       precious resources of the DSN can go
                       further. In addition, by placing more
                       responsibility on the spacecraft, we
                       reduce delays caused by signal travel
                       times and limited communications rates.
                       Despite the potential advantages, it is
                       easy to see that onboard decision-making
                       systems entail risk for the first user.
                       If the autonomy systems on DS1 perform
                       as planned, future mission teams can be
                       more confident about leaving important
                       decisions to the spacecraft.

                       One of the powerful autonomy
                       technologies on DS1 is the navigation
                       system. It uses images of main-belt
                       asteroids viewed against the background
                       stars to compute the spacecraft's
                       position. As the spacecraft travels,
                       foreground objects (the asteroids) will
                       appear to move relative to the
                       background stars. The apparent shift, or
                       parallax, gives the navigation system
                       information from which to triangulate
                       the spacecraft position. The navigation
                       system then uses positions calculated at
                       earlier times to determine trajectory,
                       making allowances for SEP thrusting,
                       gravitational pulls of the Sun and
                       planets, and other forces. If the
                       navigation system finds that it is off
                       course, it can make a course correction
                       by adjusting the direction or duration
                       of SEP thrusting....